Sounds like you need Record Level Access control. Each Sales Person should open the database with a different account name and password. you can then use setting in Manage | Security to control which records are accessible to each user. One additional benefit of this approach is that any find performed by the user or a script will automatically omit records for which the current user does not have access. This leaves "show all records" and "show Omitted only" as the two primary ways to still pull up those records. If a user does, they are covered by a grey screen that says "no access".
See "Editing record access privileges" in FileMaker Help and check out this particular sub section: "Entering a formula for limiting access on a record-by-record basis" for a description of how to set this up.
I have a log on for them already, via the client. I'll look at the permissions.